The firing voltage for a given gas discharge path and its customary graphic representation is a function of the gas pressure p and the electrode spacing D, and are an important means for characterizing electrical discharge apparatus, when the firing probability is taken into consideration. In determining the dielectric strength of a given gas discharge path, an infinite plate capacitor and its firing characteristic are generally utilized for comparison. The practical embodiment of such discharge paths, however, has electrodes with finite dimensions.
It is sufficient for determining the right-hand branch of the firing characteristic (the Paschen curve) i.e., for investigating the so-called far breakdown region including voltage minimum, to merely arrange two plane plates parallel to each other, these plates being optionally provided at the edges with a so-called Rogowski profile. However, such an arrangement is not usable for investigating firing characteristics in the left-hand part of the Paschen curve, i.e., in the so-called near breakdown zone, because detour discharges can occur. Such detour discharges can be avoided by an electrode design with plane plate electrodes that are arranged coaxially with each other. These plane plate electrodes are bent off from each other with a radius of curvature that is small relative to the electrode spacing and are brought along the inner cylindrical insulator surface of a hollow cylindrical insulator. Therefore, a gap is always formed between the bent-off cylindrical edge zone of the electrodes and the inside wall of the hollow cylindrical insulator.
As is well known, low-pressure gas discharge paths are suitable as switches for large currents of up to about 2 MA and high voltages of up to about 100 kV. These gas discharge switches operate with a pressure of the working gas, preferably hydrogen, of less than 1 Torr with an electrode spacing of less than 1 cm and a voltage above 10 kV at the left-hand branch of the Paschen curve. Since these switches can only switch on a current but cannot switch it off again they are particularly well suited for discharging large capacitors. The gas discharge switch contains an anode and a cathode which are arranged coaxially relative to each other and form a central discharge zone, an adjacent shielding zone and an insulation zone at their edges. The shielding zone is a coaxially arranged ring-cylindrical canal. The electrodes are radially bent off in the insulation zone and are each connected to one of the flat sides of a washer-shaped insulator. In the insulation zone, at the inner edge of the insulator, the spacing of the electrodes in their axial direction is approximately as large as at the discharge path. In this known arrangement, there is the danger of a breakdown at the insulator (proc. IEE, Vol. III, No. 1, January 1964, pages 203 to 213).
Gas discharge switches with coaxial bore holes in the electrodes, so-called pseudo spark switches, can be controlled by a pulsed low-pressure gas discharge. The main discharge is initiated by a hollow-cathode discharge and is fired by injection of charge carriers For this purpose, a control apparatus is provided which contains a cage which is provided with holes and surrounds the cathode backspace. The discharge path is separated by the cage from the zone of a preionization discharge, i.e., a glow discharge. Between the cage and the zone of the glow discharge, various auxiliary electrodes for shielding and potential control can further be provided Such a switch is described in Sci. Instr. 19 (1986), The Inst. of physics, Great Britain, pages 466 to 470.
In a known gas discharge switch (U.S. Pat. No. 4,335,465) for accelerating electrons and ions, a larger number of electrodes that are provided with coaxial bore holes are arranged coaxially to each other at a relatively small spacing. The electrodes at the ends of the stack and optionally a part of the inner electrodes also are connected to a d-c voltage. In this known arrangement, however, the insulator is in "direct view" of the discharge path, so that vapor deposition on the inside surface of the insulator and irradiation by photons from the discharge zone are possible.
There is a need to provide an improved gas discharge switch with electrodes that are arranged parallel to each other and are provided with coaxial holes.